I am currently performing a load calculation for a 240V feeder which supplies auxiliary loads in a MV generator (heaters, lighting, pumps, etc...) Without an accurate up to date inventory of all the loads we monitored the feeder with a meter for a few hours with both the generator running, and idle, in order to capture the maximum loading. We found that the maximum loading on this circuit was 17A during the monitoring period.
There are (4) of these generators and we are re-installing feeders to these generators from a new panel which is going to be added. (Abandoning current feeder configuration) So there will be a new 240V panel with feeder breakers out to each of the (4) generators with spare breakers in the panel available for receptacles that may be added in the room where the panel is located. I had a couple of questions that I wanted to get input on.
1) There are receptacles located in the generator enclosures that did not have anything plugged into them during our monitoring period. How would you account for any additional load that my be plugged into receptacles? Is there a standard VA rating that can be applied to receptacles in the load calc for this application?
2) Same as #1 above the new panel that that is being installed to feeder the generator aux loads will have spare breakers available for receptacle and "general use" within the room where the panel will be located. For this case is there a load rating or multiplying factor that you would add to the panel load calc to account for these future loads? Or is this just a matter of using your calculated loads and selecting a panel size that has spare room to handle any future loads?
3) When selecting the panel size I'm thinking that we would add up the loads (17A * 4 = 68A) and select a panel size that would be big enough and still have spare capacity for adding receptacles etc... as I mentioned above. In this case would 100A panel be adequate leaving only 22A for spare future loads, or should a 200A panel be chosen?
4) The 240V panel will be fed from an new upstream 480V-240V transformer. What is the rule of thumb for selecting this transformer size based on the downstream loading. For example lets say I end up selecting a 200A panel, should I size the transformer for the full capacity of the 200A panel, or only the calculated load on this panel based on the above discussions? What is the typical loading factor of a transformer when selecting the size of the transformer. For instance should you select a transformer size that is as close as possible to the calculated load, or to you select a large size to leave spare capacity for future loads (25%, 50%, etc.. spare capacity).
Thanks for the help.
There are (4) of these generators and we are re-installing feeders to these generators from a new panel which is going to be added. (Abandoning current feeder configuration) So there will be a new 240V panel with feeder breakers out to each of the (4) generators with spare breakers in the panel available for receptacles that may be added in the room where the panel is located. I had a couple of questions that I wanted to get input on.
1) There are receptacles located in the generator enclosures that did not have anything plugged into them during our monitoring period. How would you account for any additional load that my be plugged into receptacles? Is there a standard VA rating that can be applied to receptacles in the load calc for this application?
2) Same as #1 above the new panel that that is being installed to feeder the generator aux loads will have spare breakers available for receptacle and "general use" within the room where the panel will be located. For this case is there a load rating or multiplying factor that you would add to the panel load calc to account for these future loads? Or is this just a matter of using your calculated loads and selecting a panel size that has spare room to handle any future loads?
3) When selecting the panel size I'm thinking that we would add up the loads (17A * 4 = 68A) and select a panel size that would be big enough and still have spare capacity for adding receptacles etc... as I mentioned above. In this case would 100A panel be adequate leaving only 22A for spare future loads, or should a 200A panel be chosen?
4) The 240V panel will be fed from an new upstream 480V-240V transformer. What is the rule of thumb for selecting this transformer size based on the downstream loading. For example lets say I end up selecting a 200A panel, should I size the transformer for the full capacity of the 200A panel, or only the calculated load on this panel based on the above discussions? What is the typical loading factor of a transformer when selecting the size of the transformer. For instance should you select a transformer size that is as close as possible to the calculated load, or to you select a large size to leave spare capacity for future loads (25%, 50%, etc.. spare capacity).
Thanks for the help.